A Level H2 Biology Evolution Diversity Quiz

Answer Key - A-Level Biology H2 Quiz: Evolution Diversity

Section A: Foundations of Evolution

1. Definition: The process where organisms better adapted to their environment tend to survive and produce more offspring. Conditions: (1) Variation in traits, (2) Heritability of traits, (3) Selection pressure/differential survival. [3]
2. Homologous: Similar anatomy due to common ancestry but may have different functions (e.g., pentadactyl limb in humans and whales). Analogous: Similar function but different evolutionary origin due to convergent evolution (e.g., wings of insects and wings of birds). [4]
3. High mutation rate $\rightarrow$ creates high genetic variation in the viral population. Some mutations may randomly confer resistance to the drug. Under the selection pressure of the drug, resistant strains survive and replicate, leading to a population of resistant viruses. [3]
4. Genetic Drift: Random change in allele frequencies, especially in small populations (e.g., bottleneck). Difference: Drift is stochastic/random; Natural Selection is non-random and based on fitness/adaptation. [4]
5. Adaptive Radiation: Rapid evolution of diversely adapted species from a common ancestor. Example: Finches arrived at Galapagos $\rightarrow$ occupied different niches (seeds, insects, nectar) $\rightarrow$ selection for different beak shapes $\rightarrow$ speciation. [4]
6. Divergent: Related species evolve different traits due to different environments (leads to homology). Convergent: Unrelated species evolve similar traits due to similar selection pressures (leads to analogy). [4]
7. Gradualism: Evolution occurs at a slow, steady rate over long periods. Punctuated Equilibrium: Long periods of stasis interrupted by brief periods of rapid evolutionary change. [3]

Section B: Speciation and Diversity

8. Process: Geographic isolation $\rightarrow$ prevention of gene flow $\rightarrow$ different selection pressures/mutations in separate populations $\rightarrow$ accumulation of genetic differences $\rightarrow$ reproductive isolation. Example: Darwin's finches or squirrels separated by the Grand Canyon. [5]
9. Sympatric: Speciation within the same geographic area. Mechanism: Polyploidy (common in plants) creates instant reproductive isolation; or behavioral isolation (different mating seasons/preferences). [4]
10. Reproductive Isolation: Biological barriers that prevent members of two species from producing fertile offspring. Pre-zygotic: Occurs before fertilization (e.g., temporal, behavioral). Post-zygotic: Occurs after fertilization (e.g., hybrid sterility/inviability). [4]
11. Different calls $\rightarrow$ females only respond to specific calls $\rightarrow$ non-random mating $\rightarrow$ reduction in gene flow between groups $\rightarrow$ genetic divergence $\rightarrow$ speciation. [3]
12. Biological species concept relies on the ability to interbreed and produce fertile offspring. Asexual organisms do not interbreed; fossils cannot be bred. [3]
13. A small group starts a new population $\rightarrow$ only a fraction of the original gene pool is present $\rightarrow$ reduced genetic diversity $\rightarrow$ increased risk of inbreeding or fixation of deleterious alleles. [3]
14. Traits (e.g., peacock's tail) are selected because they indicate fitness to mates $\rightarrow$ increased mating success outweighs the cost of predation risk or energy expenditure. [4]

Section C: Molecular Evidence and Classification

15. Morphology can be misleading due to convergent evolution (analogous structures). Cytochrome c is a highly conserved protein; differences in amino acid sequences reflect mutations accumulated since divergence, providing a direct molecular record of ancestry. [4]
16. Assume a constant mutation rate (molecular clock). Count differences in base pairs between two species. The greater the number of substitutions, the longer the time since they shared a common ancestor. [4]
17. Cladogram: A branching diagram showing the evolutionary relationship between species. Node: Represents the most recent common ancestor of the lineages branching from it. [3]
18. Monophyletic: Includes the common ancestor and all its descendants. Paraphyletic: Includes the common ancestor but excludes one or more descendant groups. [4]
19. rRNA is present in all living organisms (universal). It performs a critical function (protein synthesis), so it evolves very slowly. This allows for the comparison of very distantly related taxa (e.g., Bacteria vs Archaea). [4]
20. Use fossils to determine the absolute date of a known divergence event (e.g., 50 million years ago). Calculate the number of mutations between those two groups. This establishes the "rate" of mutation per million years, which can then be applied to other sequences. [4]